Cook pasta according to directions. Meanwhile, in a large skillet, saute mushrooms and onion in 1 TB butter until tender.
In a large bowl, beat ricotta and 4 oz of cream cheese until blended. Stir in 1/2 cup Asiago cheese, parmesan cheese, bacon, 1 TB parsley, garlic salt, nutmeg, pepper, and mushroom mixture. Spoon into shells; place in a greased 13x9 inch baking dish.
In a large saucepan, melt remaining butter. Stir in flour until smooth; gradually add the cream, broth, and milk. Bring to a boil; cook and stir for 1-2 minutes or until thickened.
Stir in Romano cheese and the remaining cream cheese, Asiago and parsley. Pour over shells. Sprinkle with mozzarella cheese. Cover and bake at 350 degrees for 30 minutes. Uncover; bake 10-15 minutes longer until bubbly.